fix or remove Ultrascale SDRAM init about misoc HOT 4 CLOSED

Sayma uses the ARTIQ 4 bootloader currently (and there's no particular reason I know for it to go back). The Ultrascale SDRAM code in MiSoC could be useful for other people who use MiSoC on Ultrascale, not that any necessarily exist.

from misoc.

I don't fully understand the implications of these different paths. Are you proposing switching LM32 to mor1kx? Where would Ultrascale SDRAM support be housed if not in MiSoC? What caused it to stop working?

from misoc.

ARTIQ 4 no longer uses the MiSoC bootloader, and Ultrascale development continued in the ARTIQ bootloader but the changes were not ported to the MiSoC bootloader.

from misoc.

Since Sayma support is part of ARTIQ 4 it seems like Sayma ought to also use the ARTIQ 4 bootloader. What are the prospects for this port?

from misoc.